We know when $0 \lt \theta \lt \frac{\pi}{4}$, $\cos\theta \gt \sin\theta$
Also, all the terms $a,b,c,d$ are multiplication of an exponential term (which is always positive) and a logarithmic term either $\log_2\cos\theta$ or $\log_2\sin\theta$
Now, both $\sin\theta$ and $\cos\theta$ are fractional values in $0 \lt \theta \lt \dfrac{\pi}{4}$ range
So, both$\log_2\cos\theta$ and$\log_2\sin\theta$ will definitely be negative
So, $a,b,c,d$ all are negative terms
Now, let's compare $a,b,c,d$
i.) $a$ and $d$:
$\dfrac{a}{d}=\dfrac{((\sin\theta)^{\sin\theta})(\log_2\cos\theta)}{((\sin\theta)^{\sin\theta})(\log_2\sin\theta)}$
or,$\dfrac{a}{d}=\dfrac{(\log_2\cos\theta)}{(\log_2\sin\theta)}$
Since,$\cos\theta \gt \sin\theta$
or,$\log_2\cos\theta \gt \log_2\sin\theta$ (as $\log_ax$ is an increasing function for $a \gt 1$)
or, $\dfrac{\log_2\cos\theta}{\log_2\sin\theta} \lt 1$ (as both $\log_2\cos\theta$ and $\log_2\sin\theta$ are negative)
or, $\dfrac{a}{d} \lt 1$
or, $a \gt d$ (as $a$ and $d$ both are negative) ------(1)
ii.) $b$ and $d$:
$\dfrac{b}{d}=\dfrac{((\cos\theta)^{\sin\theta})(\log_2\sin\theta)}{((\sin\theta)^{\sin\theta})(\log_2\sin\theta)}$
or,$\dfrac{b}{d}=\dfrac{((\cos\theta)^{\sin\theta})}{((\sin\theta)^{\sin\theta})}=\left(\cot\ \theta\ \right)^{\sin\ \theta\ }$
Now for$0 \lt \theta \lt \frac{\pi}{4}$,$\cot\theta$ greater than 1 always
So,$\dfrac{b}{d} \gt 1$
or, $d \gt b$(as $b$ and $d$ both are negative)-------(2)
iii.) $a$ and $c$:
$\dfrac{a}{c}=\dfrac{((\sin\theta)^{\sin\theta})(\log_2\cos\theta)}{((\sin\theta)^{\cos\theta})(\log_2\cos\theta)}$
or,$\dfrac{a}{c}=\left(\sin\theta\ \right)^{\sin\ \theta\ -\cos\ \theta }$
Now,$\sin\theta\ -\cos\theta$ is a negative term and$\sin\theta$ has a fractional value
So, $\left(\sin\theta\right)^{\sin\theta\ -\cos\theta\ }$ will definitely be greater than 1 (as fractional term having negative power is always greater than 1 )
So, $\dfrac{a}{c} \gt 1$
or, $c \gt a$ (as both a and c are negative) --------(3)
So, from (1),(2) and (3),
$c \gt a \gt d \gt b$
So $a,b,c,d$ are now arranged in descending order.
Also, there are 4 terms in total.
So, median = average of $3^{rd}$ term and $4^{th}$ term =$\dfrac{a+d}{2}$