The technology sector experienced fast-paced growth in 2020, as investors looked to tech companies as a safe place to grow their investments during the pandemic. The U.S. hasn't put the coronavirus crisis behind it yet, but some investors are already looking beyond the tech sector for new areas of growth as the economy begins to open back up. This has caused the share prices of some tech stocks to fall from their highs, creating good buying opportunities for investors interested in Roku (NASDAQ: ROKU), Okta (NASDAQ: OKTA), and The Trade Desk (NASDAQ: TTD). Here's why. Image source: Getty Images. Roku's video-streaming platform is firing on all cylinders Roku's share price is down about 10% over the past three months, and while it may not be cheap in the traditional sense of stock valuations, this dip has created an opportunity for investors to buy the video-streaming specialist's shares at a slight discount. Roku is coming off of a phenomenal year of growth, ending its fourth quarter with 51 million active users (up 58% from Q4 2019) and sales growth of 58% year over year. The company has benefited from an influx of video-streaming services (think Netflix, Hulu, Disney+, Amazon, HBO Max, etc.) that all use Roku's platform to deliver their content to users. Roku makes money when users sign up for a streaming service through its platform, so the more video-streaming subscriptions available, the better. Roku's average revenue per user increased 24% in 2020, indicating that users are signing up for more services than ever before. But even if that trend slows down (you can only sign up for so many services, after all), the company still has other growth opportunities, including advertising. Monetized video ad impressions more than doubled in the fourth quarter of 2020, and Roku just announced last month that it's buying Nielsen's advertising platform. This should boost the company's ability to sell ads and help it tap into the connected-TV ad market, which eMarketer projects will be worth $18.3 billion by 2024 (up from $11.4 billion this year). Roku's video-streaming platform has more users than ever before, it's earning more money from those users, and the company is tapping further into the growing connected-TV ad market. Add to all of that the fact that Roku's shares are down over the past three months, and the company's stock looks like a good buy right now. The internet needs more safety and Okta is helping Companies are desperately trying to find new ways to manage their websites and data so that their users and employees only have access to the information that they're supposed to have access to. This online gatekeeping has become even more important after many people started working from home last year. That's why Okta's identity and access management (IAM) services are a no-brainer for many businesses. Okta's platform allows users to log in to their accounts safely and helps them retrieve access when they've been locked out, making online account management much easier for IT teams. For Okta, the opportunity is huge. The company says its total addressable market in IAM is currently $55 billion and will soon reach $80 billion. Okta is successfully tapping into this space, with fiscal 2021 (which ended on Jan. 31) sales increasing 43%, subscription revenue jumping 44%, and the number of customers with annual contracts worth $100,000-plus up by 33% year over year. Investors have an opportunity to tap into Okta's recent growth right now, as its share price is down about 2% over the past three months. But don't expect the company's stock to stay stagnant for long. Okta's management estimates that revenue will increase 30% in fiscal 2022, and as the company continues to grow, I suspect investors will flock back to Okta's stock. The Trade Desk taps into the massive advertising market If you're unfamiliar with The Trade Desk, the company has a robust advertising platform that businesses use to put their targeted ads all across the internet and connected TVs. The Trade Desk makes money by taking a cut of the advertising dollars its users spend on its platform. And with the global digital advertising market estimated to be worth $526 billion in 2023, those small slices of ad spending add up fast. The Trade Desk's revenue spiked 48% in the most recent quarter and the company's adjusted EBITDA margin expanded to 48%, up from 39% in the year-ago period. Not only are its sales and margins moving in the right direction, but The Trade Desk has reported a high retention rate for its customers -- 95% -- each quarter for six consecutive years. Some may be wondering what will happen with the company as Apple and Alphabet's Google begin to move away from online cookies, which track users and are used for targeted ads. But some investors' fears may be overblown. The Trade Desk is working with Google and others on an alternative to cookies, which will allow for both targeted ads and increased online privacy for users. Even with some near-term effects from the shift away from cookies, The Trade Desk's management still estimates that sales will grow 34% at the midpoint of guidance in the first quarter of this year. The Trade Desk is one the top independent ad-buying platforms, and with its stock currently down 11% over the past three months, now looks like a good time to snatch up some shares of the company. Don't forget this last step If you buy shares of any of the companies above, remember this one last investing step: Hold the stock for years. Tech stocks, in particular, have a habit of riding the market's waves and can tempt even the most steadfast of investors to reach for the sell button. But these stocks should be able to outpace the broader market's returns in the coming years if you can remain patient. Find out why The Trade Desk is one of the 10 best stocks to buy now Motley Fool co-founders Tom and David Gardner have spent more than a decade beating the market. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.* Tom and David just revealed their ten top stock picks for investors to buy right now. The Trade Desk is on the list -- but there are nine others you may be overlooking. Click here to get access to the full list! *Stock Advisor returns as of February 24, 2021 John Mackey, CEO of Whole Foods Market, an Amazon subsidiary, is a member of The Motley Fool's board of directors. Suzanne Frey, an executive at Alphabet, is a member of The Motley Fool's board of directors. Chris Neiger owns shares of Apple. The Motley Fool owns shares of and recommends Alphabet (A shares), Alphabet (C shares), Amazon, Apple, Netflix, Okta, Roku, The Trade Desk, and Walt Disney. The Motley Fool recommends the following options: long January 2022 $1920.0 calls on Amazon, long March 2023 $120.0 calls on Apple, short January 2022 $1940.0 calls on Amazon, and short March 2023 $130.0 calls on Apple. The Motley Fool has a disclosure policy.Source