There is so much pressure to build and develop faster, faster, faster. The end result of the rush is a creation that can't carry it's own weight and buckles under pressure. It's important to master the pillars of web development. Effort to master the pillars will reward you with skills that stand the test of time as well as creations that users will enjoy.
I'm an engineer and I work in the construction industry. I see many parallels between constructing a building and constructing a website. On my own journey to learn web development, I've flitted between shiny frameworks, but have come to see there are four pillars...foundation, structure, form, and power. Not being intimate with each of them puts any skills with a framework on shaky ground.
Solid HTML is the next important piece. HTML is the skeleton, keeping everything upright. It's the floors and shearwalls. If you do it right, your site will function and be useful to someone on an enormous range of devices, some of which may not have a screen. A key point is that HTML should explain what the elements of the site ARE (or should be), not what they should look like...that's the job of CSS. Spend some time laying out your information and give it good structure. You'll have a solid fallback.
CSS breathes life into the HTML skeleton. Like the exterior envelope of a building, it gives form, colour and shape. Responsive design principles are brought in through CSS. There's a lot of beauty that can be brought to bear with CSS on its own. Take some time to learn its nuances thoroughly and gain appreciation for its capabilities. Don't use HTML where you should be leveraging CSS to create the look and feel you want.
There's a rush today that makes everything frantic and borderline unsustainable. The rush, when applied to web design, can result in products which are difficult to maintain and perform poorly for their intended audience. Take your time, smell the flowers, and make sure your creation has a solid footing with the pillars of web technology.